


My Roommate Is The Devil

by PandoraButler



Category: Ao no Exorcist | Blue Exorcist
Genre: AU, Alternate Universe, Amaimon x Yukio? Kinda?, Demon Kings, Don't Ask Questions, Fluff, I Ship It, M/M, Uhm, ao no exorcist - Freeform, blue exorcist - Freeform, gay demon babies, hamster amaimon is best amaimon, i have no idea how to tag things, idk - Freeform, it sails, mephishiro, whatever
Language: English
Status: In-Progress
Published: 2018-01-15
Updated: 2018-01-26
Packaged: 2019-03-05 02:44:01
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 4
Words: 4,947
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13378440
Author URL: https://archiveofourown.org/users/PandoraButler/pseuds/PandoraButler
Summary: Shiro was having a hard time finding a roommate until one day his roommate found him. However, this strange male wasn't your average guy. Nope. He was none other than a demon king!





	1. Prologue

**Author's Note:**

> I know Mephisto isn't /the/ devil but the title was funnier this way. 
> 
> #NoRegrets

Shiro sighed before sitting down in a chair at his favorite cafe. It had been only a few days since he moved into his apartment and now it seemed like he would have to move all over again! Why did he decide to live in the most expensive area in town? What was he thinking?! If he didn't find a roommate soon (and he hadn't had any luck thus far) he would be living on the streets! He'd talked to practically every human being under the sun. Best friends, old friends, new friends, and even strangers! But, he wasn't having any luck. Everyone he knew (and even those he didn't but asked anyway) already had a roommate!

"Wow, you aren't looking too good," a stranger said. He was a dapper looking fellow wearing practically all white. The parts of his clothing that weren't white were purple. It was a rather strange combination. Shiro was reminded of a clown, although he wasn't sure if clowns would be complimented or offended by that thought. "Have a cupcake!" The male pushed a cupcake across the table that said 'Merry X-Mas' on it. It wasn't Christmas. It wasn't even  _close_  to Christmas, but Shiro didn't refuse the cupcake. He needed something to boost his spirits. 

As Shiro nibbled on the cupcake, after not even bothering to check for poison, the stranger continued to speak. "So, what's bugging you? Did you get dumped? Divorced? Lose a job? Oh! I've got it! Your family just found out you were gay, didn't they?"

"None of the above," Shiro mumbled as he ate the last bite of his cupcake. "I'm not gay," he began. The stranger raised his eyebrow and smirked as if to say 'as far as you know, but clearly you haven't met me.' "I'm demi and looking for a roommate, since I'm an idiot that decided to move into a place I can't afford."

"Well, you're in luck! Because I'm looking for a place to live till I find a satisfactory vessel for the devil!" the stranger grinned. He was quite pleased with himself, so it seemed, but Shiro couldn't tell if he was serious. The guy didn't look like he was joking, did Shiro just hear him wrong?

"You didn't hear me wrong," the stranger said, as if reading Shiro's mind. A business card appeared in his hand and he gave it to Shiro. It had a little dog in the bottom right-hand corner with the words 'Legendary Demon King: Mephisto Pheles! Son of Satan and King of Time!'

"So, how about it? Would you like to be my roommate?" Mephisto asked. 

Shiro put the business card in his pocket and grabbed Mephisto's hand. "I don't discriminate. You're a blessing! I've finally found a roommate!" he said as tears rolled down his face. He was too happy to contain his emotions. He wouldn't be living on the streets just yet!

"A blessing?" Mephisto laughed. "Don't you mean 'curse'? I'm certainly not a gift from heaven." 

"As long as you pay the rent on time, I don't care what you are!" Shiro said. "But, please don't summon your father in the apartment. I don't know how I'll explain that to people."

Mephisto leaned back in his chair and laughed his head off. This human wasn't phased at all by the fact that he said he was a demon. To be honest, Mephisto wasn't entirely sure that Shiro believed him, but he didn't care. He found his place to stay and this guy had found a roommate he was looking for! Everyone was happy in the end, right?

"My name is Shiro. I look forward to rooming with you."

"And I look forward to rooming with you too," Mephisto replied. The two of them might regret meeting in the future but, for now, neither of them cared what the future had to bring. One crisis was averted, who knows how many more would come?


	2. Kapitel Eins

Mephisto stood in the empty lot watching as the blue flames consumed the body before him. This was just another one of his many failed attempts to summon Satan. He'd been so used to listening to his father's wishes that he'd forgotten the reason why he was fulfilling them in the first place. Was there a reason? Or was it just habit at this point?

The demon had failed, yet again, with his attempts. This person wasn't strong enough to hold Satan. It would seem that no human was strong enough to hold Satan. This would be a long and tiresome search. It had already been a few weeks since he'd started. Mephisto's roommate, Shiro, didn't seem to worry too much about what Mephisto did. Mephisto couldn't decide if that was a good thing or a bad thing. In any case, it meant that he wouldn't have to come up with bogus excuses or explanations. That was a relief. But, Mephisto couldn't help but feel a bit sad that the guy he just met (and instantly wanted to get to know better) didn't seem to care about him in the slightest. This wasn't the first time Mephisto had fallen for a human, and it probably wasn't the last time either. The demon liked to think that he was just an avid lover of humanity as a whole, even though that was only  _partially_ true. Yes, the demon did have a soft spot for the stupid creatures, but he also had a soft spot for  _specific_  stupid creatures. It would seem that Shiro had become one of the  _specific._

The body stood up and lunged for Mephisto. This wasn't anything new, he'd had to avoid the flames before on the previous attempts too, but this time the body actually managed to hit him. A small blue flame burned on Mephisto's torso. It hurt like Gehenna itself but there was nothing Mephisto could do about it anymore. He took his umbrella and shot the body in the head, exactly three times, before turning around and leaving it behind to be destroyed fully by the flames of Satan. It was better to kill the vessel than to just assume that it would die on its own.

The flame had disappeared just before Mephisto got back to the apartment. He knocked on the door (because he had forgotten his key, again) and waited for his angry roommate to come and answer. It didn't take long before he did.

"Mephisto! I've told you countless times that you need  _two_  keys to get back into the apartment. What would you have done if I wasn't here? You idiot! Stop forgetting the second key! It's a pain to have to stop what I'm doing every  _single_  time just to answer the door because you're an idio-" Shiro stopped scolding Mephisto when he saw blood ooze out of a tear in his clothing. "Did you get shot? What happened? Are you okay?!" Shiro asked. He promptly helped Mephisto inside the apartment and sat him down in the bathroom, right next to the first aid kid, and got to work.

"I'm fine, it just hurts a lot. You don't have to do anything. And no, I didn't get shot," Mephisto tried to stop Shiro before he touched the injury, but nothing he said impacted Shiro's actions. Before Mephisto knew it, Shiro had already taken off most of the clothing that covered Mephisto's upper body and had begun dabbing  the wound with a cotton-ball covered in, what Mephisto thought to be, alcohol. 

Mephisto cringed, "What do you think you're trying to do to me?! I just told you that you don't have to do this!" he snapped. Shiro didn't seem the slightest bit concerned.

"Listen, I don't care what you think you are," Shiro pointed to the wound, "but that clearly is a human wound and needs to be treated as such. So grow a pair and let me disinfect it since I  _know_  you won't let me take you to the hospital." Mephisto stopped fighting back and allowed Shiro to do whatever it was he intended to do. He didn't like it, but Shiro had a point. The blue flames leave wounds that a demon's body can't heal quickly. It would heal at the same rate a human's wound would. Mephisto regretted the fact that he hadn't sped up time on the wound to make it heal before returning back here. He could've avoided this whole conversation, but he was tired and didn't want to get to that level of exhaustion.

"Are you a member of a gang or something?" Shiro asked. Mephisto chuckled. He knew that sooner or later Shiro would ask about him. Curiosity always wins with humans. Mephisto was just surprised at how long it had taken Shiro to ask.

"Sure, if you want to think of it like that," Mephisto began, "but I've already told you what I am and what I'm doing." Shiro and Mephisto held eye contact for a few minutes but neither individual said a single thing. Shiro looked away only to apply the final bandage on Mephisto's body. 

"I don't understand," Shiro started. "What exactly about you makes you a demon? Is it your pointy ears and teeth? The fact your hair is purple? Your mischievous eyes and grin you always have on your face? Or maybe it's just your weird sense in fashion? No matter what kind of explanation you give me, I won't understand. You just don't seem like a demon to me. If anything, you're an angel wearing a devil's mask."

Mephisto laughed and laughed until tears escaped from his eyes. There was truth in what Shiro said but it was simply because  _Shiro_  had said it that made the words all that much more  _hilarious._ The demon laughed at the fact a  _human_  could notice so much about him when they hadn't even known each other that long. He didn't know what was more disgraceful: the fact he wasn't demonic enough or the fact that Shiro, a human, knew he wasn't.

The demon stopped laughing and held his head in his hands. Painful memories flooded back from the depths of his forgotten past and invaded his thoughts. Feelings he'd sworn never to feel again came back to him. Pandora's Box had opened and Mephisto silently sobbed. It's the truth that hurts, because with the truth you realize all of the lies that were told. Mephisto never wanted to be a demon. He never wanted to hurt people. At most all he wanted to do was to play a few pranks on them. But simply because of who he was, or who he was the son of, he'd been cast from heaven like all of the others. His wings were torn off and he was forced to become dealer in lies. 

How many years had it been? After all this time, why had  _Shiro_  been the one to notice his facade?


	3. Kapitel Zwei

Shiro was experiencing a crisis. A very terrible disaster. His roommate, who he had just recently acquired, was crying before him. Now, he could wing it and try and comfort the guy (when he didn't even understand why he was crying in the first place) or he could back away slowly and pretend that Mephisto wasn't crying and that everything was perfectly okay.  _Or_  he could continue to stand here awkwardly, as everyone usually does, and continue thinking about what he  _should_  be doing. Yeah, that's the real way to go. 

"I'm sorry you had to see me like this," Mephisto's voice was quiet, like a whisper, but Shiro could still hear his words. "Could you give me some time by myself?" he asked. Shiro nodded and closed the bathroom door on his way out. In his rushed state, he'd forgotten to put away the first-aid kit (but he did remember to take Mephisto's clothes for some reason). The demon stood up and gathered the items to return them to their rightful spot. He stared at himself in the mirror. He was angry with himself. He was frustrated. He hadn't  _felt_ anything all this time, so why  _now?_  It was the worst of times to cry. Demons shouldn't cry or  _need_  to cry. Demons shouldn't  _feel_. 

Mephisto washed his face and blew his nose. He sat on the floor, back leaning against the door, and stared at the ceiling. All of what he had felt left him. He was empty now. There was no emotion left to  _feel_. There were no more tears left to shed. He was a blob of forgotten feelings that weren't so forgotten. 

Shiro paced in the living-room as he waited for Mephisto to come out. He didn't know what to say. Should he apologize? Should he pretend nothing happened? Shiro was just a roommate. He didn't have the right to know anything about Mephisto. He shouldn't demand answers, even though he really wanted them. Did Shiro say something he shouldn't have? Was it actually really insulting to a demon to be called an angel? Shiro felt a wave of guilt wash over him. He didn't mean to offend his roommate. He was just asking questions. Shiro cursed at himself. Why did he even  _ask_  those questions?! He'd promised himself he wouldn't ask anything! He thought that Mephisto would eventually bring it up all on his own one day, but curiosity got the better of him since Mephisto came back injured. 

"I know he came home injured but why did I say something like  _that_?" Shiro mumbled. He stopped pacing and felt his cheeks tint red. He had just said 'home'! This wasn't Mephisto's home! This wasn't a home for either of them! This was a living arrangement. Shiro sighed. He was already becoming attached to Mephisto and they hadn't even known each other for long. When did Shiro start thinking of this place as a 'home'? Why did he want that demon to feel so welcome? 

The door to the bathroom opened and Mephisto stepped out. His poker face held no clues that he'd cried. Shiro would've begun to think he'd imagined the whole thing if it wasn't for the redness of Mephisto's eyes. Mephisto placed a hand on the door-frame and gripped it so tightly that his knuckles turned white. Shiro wasn't sure if he was suppressing anger or was just too wobbly to stand. What was going on with his roommate?

"You need to leave," Mephisto said. His voice was devoid of any emotional signs. The guilt Shiro felt only got worse. He had to apologize. He wanted to say something, but the minute his mouth opened Mephisto cut him off, "Don't apologize, just  _leave_." Shiro noticed Mephisto's black nails grow as he continued to grip the door-frame. Something was wrong with him, but what? 

Blue lines, similar to veins, peeked out from underneath the bandage on Mephisto's torso. They spread across his body as Mephisto's eyes, ears, and teeth changed right along with his nails. His teeth grew sharper. His ears grew longer. His eyes were tinted blue and Shiro thought for sure he saw a small blue flame in them. The same flame he'd seen in Mephisto's eyes consumed Mephisto's whole body. Shiro was frozen in place. He was shocked (as well as a bit terrified) and had no ideas of what to do next. Mephisto had called himself a demon and Shiro thought he understood, but now he realized that he didn't understand a single thing. 

Mephisto's aura changed. His poker face became a sadistic grin which revealed his sharper teeth. Whoever it was in that body, Shiro knew for sure it wasn't Mephisto. "I thought they were lying when they told me he had a new pet," Mephisto's voice said. Shiro cringed. It sounded like him, but he knew it wasn't him at all. "Don't look so surprised," the stranger continued, "I'm sure my son told you who he was when you first met, did you think he was joking?" the stranger laughed in such a manner that caused the hair on Shiro's neck to stand up.

"Satan?" Shiro asked.

"The one and only," he bowed. Bloody tears fell down the sides of Mephisto's cheeks but Satan didn't seem too concerned. "We better make this quick or you won't have a roommate any longer," he laughed. 

"How can you be so nonchalant about your own son's body?!" Shiro frowned.

Satan laughed again, "Son? Mephisto may be related to me by blood but he is by no means a son in my eyes. He is a tool, one of the best tools I have, and I won't kill him. I haven't killed him so far and I don't intend to, yet. But enough about him, I'm here about you. I'd like to make a deal with you," Satan pointed one of his long fingernails at Shiro.

"A deal?"

"Yes, a deal. If you promise to become my vessel when I need you, I'll promise to leave Mephisto alone. If you refuse, I'll add more scars to his collection. Something tells me you won't care if I threaten to kill you, but you  _will_  care if I threaten to harm  _him_."

"What scars?" Shiro regretted the question moments after he asked it. Satan's grin only got worse. The flames temporarily revealed all the scars that Mephisto would've had, if he hadn't reversed time on his body. Needless to say, Shiro was shocked. Scars overlapped scars until Mephisto's skin was hardly recognizable, his face was no exception.  

"Beautiful, aren't they?" Satan stared at Mephisto's arms and hands. "I've always hated his little time-trick. It only made me want to give him more since he kept erasing them."

Shiro wasn't sure how he felt about demons, but he knew now that he simply  _hated_  Satan. "I accept your offer, if you heal Mephisto's wound before you leave his body."

"Fair is fair," Satan smiled. He tore off Mephisto's bandage and flames swarmed around the wound to patch it. It was because of this wound that Satan was able to possess him. Now that he'd gotten what he wished, he didn't need to possess Mephisto anymore. Satan stepped towards Shiro and touched the center of his forehead. With that touch, a small blue flame traveled down his body and to the sole of his foot (because Satan has a sense of humor) where it would leave a mark of possession. As long as Shiro wore socks, Mephisto would never know that he was marked the devil's vessel.  

Mephisto's eyes closed as his body returned to normal. He fell forward (into Shiro) but his roommate caught him and he never touched the ground. Shiro stared at the perfect skin. It was such a contrast to the skin he'd just seen. How many times had he had to endure his father's torture? Shiro shuddered at the thought. The only scars that remained on him now were two marks on-top of his shoulder blades. They appeared to be burn marks, but they were far too symmetrical to be any ordinary burn. Shiro could only make one assumption: Mephisto  _had_  been an angel. It wasn't that his words were insulting, Shiro realized, it was that his words had been  _true_.

Shiro held Mephisto's limp body close and sobbed. His roommate wasn't a demon and shouldn't have been made into one. His roommate shouldn't have had to deal with the cruelty of Satan as a father. He hadn't known Mephisto for long, but it was in this moment that he decided: even if the universe hated Mephisto's guts, Shiro would make up for all that hatred with his love.

"Shiro? Why are you crying? Did he hurt you? Are you okay?" Mephisto asked. He began to back away from Shiro's hold but Shiro just held him tighter.

"I'm fine," he said, "I'm perfectly fine," he sobbed. 

The demon wasn't fully convinced but he didn't refute Shiro's statement. Mephisto wrapped his own arms around Shiro to hug him. Mephisto had just been possessed and controlled by Satan, but the first thing he did when he regained consciousness was worry about Shiro, this only made Shiro cry more.

"Are you sure you're okay?"

"Yes," Shiro sniffled, "I'm certain."


	4. Kapitel Drei

Mephisto turned into an alleyway on his way back to the apartment. He was carrying two bags filled with different types of ramen noodles. Shiro wouldn't like it, but Mephisto didn't care. He wanted ramen; he would eat ramen. Ramen had been his guilty pleasure since the night Satan had possessed him. He  _needed_  ramen in his life.

A male with blonde hair and pale skin leaned up against the brick wall of a building nearby. Mephisto avoided eye contact and kept walking. He saw him, he knew him, but he didn't have to talk to him. The male, slightly annoyed, walked beside Mephisto. Mephisto, being the jerk that he is, started walking faster. The male, also being the jerk that he is, walked faster too. Each individual picked up their pace until they both were out of breath and outside the apartment's door. Mephisto, cursing himself for forgetting the second key again, knocked. 

Mephisto, fully prepared to be scolded by Shiro for forgetting his key, was shocked when that didn't occur. He was so shocked that he'd forgotten the blonde fellow was following him and walked right into the apartment to set the bags of ramen down on the kitchen counter. 

"Are you going to tell me who this stranger is?" Shiro asked.

"No one of importance," Mephisto smiled and started 'gently' pushing the blonde in the direction of the door. The blonde stood his ground and refused to leave. He hadn't come all this way just to have Mephisto kick him out before he delivered his message. 

"Don't act like you don't know me, Sa-" Mephisto covered the blonde's mouth before he could finish the name.

"If you dare call me by that name I swear I will cut off your head and put it in a jar," Mephisto threatened.

"I'd like to see you try, brother," the blonde retorted. Shiro looked at the blonde and then to Mephisto. He couldn't see the resemblance outside of the abnormal hair design. The two looked  _nothing_  alike. Shiro began to wonder how many people Satan had affairs with and if any two of his children had the same mother.

"Are you going to tell me who you are?" Shiro asked. If Mephisto wasn't going to tell him, he might as well ask the individual himself.

"My name is Lucifer. I am Mephisto's one and only older brother and the King of Light," Lucifer's deadpanned expression hadn't changed since the moment he'd walked through the apartment's door. Shiro wondered if he ever showed emotion. Did he even feel things?

"You left out the part where you're Satan's favorite soldier and do absolutely  _everything_  he asks of you," Mephisto rolled his eyes and plopped down in a chair. He glared at his brother while eating a packet of uncooked ramen.

"Why are you eating that unhealthy human food? Have you really fallen that much?" Lucifer questioned. Mephisto opened the seasoning packet, poured it onto the uncooked noodles, and took a bite without saying a word. Shiro sighed and Lucifer winced. 

"Are you going to tell me why you're here?" Mephisto asked. "The sooner you tell me the sooner you can leave. If you don't tell me within the next minute, I'll lock you in another dimension and throw away the key."

"Father wants you to stop looking for a vessel. He wants to change your mission to finding his sons."

Mephisto rolled his eyes, "Which ones? We do have a lot of siblings, or is he not aware of that fact?"

"They're half-human half-demon twins. One of them is coming of age and has inherited the blue flames. If you don't find him soon he will go rampant in Assiah and won't be of any use to us. Find him quickly, brother," Lucifer said. He had nothing else to say so he turned on his heel and left. 

Mephisto finished his block-o-ramen and stood up. He let out a long sigh and made his way to the door. "Where do you think you're going?" Shiro asked.

"You heard the fellow," Mephisto snapped his fingers and his favorite umbrella appeared in his hand. "I have to find a demon in a haystack of humans."

"Tonight? Mephisto, it's almost dark out," Shiro couldn't hide the fact that he was worried. It wasn't long ago that he'd seen the terrible Satan and now he was seeing an emotionless brother. He didn't want to stop Mephisto from doing his role as a King of Hell, but a part of him wanted to do just that.

"Would you like me to come back before midnight, fairy godmother?" Mephisto laughed. 

"I'm coming with you," Shiro said. He grabbed his coat and put on his shoes. 

"You can't come, Shiro," Mephisto began, "I can't assure your safety if this brother of mine has already gone rogue."

"I can protect myself."

Mephisto raised an eyebrow but didn't respond. Even if he tried to convince Shiro, he knew it wouldn't work. Shiro had already decided. Within a few minutes, the two had made it outside; however, Mephisto hadn't taken a single step in either direction. He opened his umbrella and looked at Shiro.

"Do you trust me?" he asked. Shiro nodded. "I need a verbal confirmation," Mephisto said before he grabbed Shiro's hand.

"Yes, I trust you."

"Good," Mephisto smiled, "because Mary Poppins doesn't do it right." The two slowly began to rise up off the ground. Shiro didn't realize what was happening until it was too late. The buildings were already so far away and the people were already so small.

"Lord Almighty, I am going to die tonight," Shiro didn't care if he cut off Mephisto's circulation, he was going to cling to his arm like there was no tomorrow. He was also going to hold Mephisto's hand so tightly that it might fall off. 

"You said you trusted me, but this doesn't feel like trust. I might lose my arm!" Mephisto laughed, "Now we begin the search for blue flames or demon-looking people. Are you ready?"

"You want me to look at the ground from this height?!" Shiro's concern was evident in his words.

"I won't let you fall, Shiro," Mephisto assured. Shiro was still unconvinced but he kept quiet. The two looked at the ground for signs but found none. Shiro didn't know how long they stayed in the air. He didn't now how much time had passed or how long the stars twinkled above them. He just knew that eventually he stopped staring at the ground and began staring at Mephisto's face. It was so close to him since he was hanging onto his arm so tightly. Mephisto's eyes glimmered in the dark as the light reflected off of them from down below. His hair moved with the wind but his hair curl didn't lose its shape. 

"You're cheating," Mephisto said. Shiro flinched. He'd been staring at him too long, hadn't he? Mephisto turned his head to look directly at Shiro. The two locked eyes and a grin made its way to Mephisto's face. "I know I told you to look for demons, but spending the night looking at me is hardly productive if you already know I'm a demon."

Shiro opened his mouth to respond but he was too late. Mephisto turned his head back to the ground immediately. A bright burst of blue appeared. Blue flames could only mean  _one_  thing. They'd found their missing demon child.

There was no time to waste. The two floating males made their way to the ground next to the flames. Mephisto landed a good distance. He was about to tell Shiro to stay away, but of course Shiro stopped him before he could say a thing. "I've already made it this far," he began, "I'm not going to leave you by yourself now." 

A boy with dark hair and pointed ears was hunched over and growling. With each step the two took forward, his voice only got louder. Another boy, not surrounded in flames, hadn't noticed Mephisto and Shiro and spent his time trying to calm the other boy down. It was too late to stop him without assistance, he was already losing his control. Mephisto got closer to the flames, but not too close. He tapped his umbrella on the ground and a giant circle appeared around the demon child. It was filled with lines and markings that Shiro didn't understand, and neither did the other boy apparently.

The demon child's voice only got louder and more strained. Mephisto ignored it and began to chant in a language unrecognizable to Shiro. "Stop it! You're hurting him!" the other boy said. He took a step towards Mephisto but Shiro grabbed his arm and lead him away. He struggled with every step but eventually gave in when he noticed Mephisto's pointed ears. If this stranger to him wanted to kill his brother, he already would have by now.

The flames got bigger as the screams got louder. However, in an instant, the noise and flames both died. The demon child fell to the ground and the circle he was trapped in disappeared. Mephisto picked him up and began walking. He didn't give an explanation, he just spoke to the other boy, "You can't stop me from taking him, so you might as well come with me." 

And with that, Mephisto, Shiro, and the twins made their way to the apartment, (even if one of them was unconscious). 

**Notes for the Chapter:**

> My writing was never good but this chapter was especially bad. I can't say it'll get better than this but I hope it does.


End file.
